Unions have waded in. Volunteers are being prepped to work at the State Fair. And e-mails and fundraising appeals are flying.

A full 15 months before Minnesota voters decide whether to cement a ban against same-sex marriage into the state Constitution, the campaign over the amendment is already heating from a simmer to a full boil.

Groups on both sides of the proposed amendment have ramped up their fundraising machinery -- amid suggestions the campaign could top $10 million -- and have boosted their efforts to enlist armies of volunteers.

But the organizing faces two daunting realities: Extravagant gushers of cash and ground troops have had little effect on voters in other states, and anti-amendment groups have been largely ineffective elsewhere in preventing the measures from passing.

A study published last year by New York University political scientist Patrick Egan found that in 33 states where marriage and domestic-partner ballot issues have been decided since 1998, the campaigns have not changed voters' minds.

Examining polling data, Egan concluded that both sides "have largely fought to a draw, in that the share of the public saying they intend to vote for or against these measures typically changes very little over the course of these campaigns."

The Human Rights Campaign, the nation's largest gay rights advocacy group, is nonetheless one of a growing number of organizations on both sides of the issue in Minnesota that are already raising money. Seven groups -- four opposing the amendment, three favoring it -- have registered with the state's Campaign Finance Board.

Representatives of the organizations declined to say how much they've raised so far or what their eventual goals will be, but based on earlier statements and the history in other states, $10 million or more could be spent between now and Election Day in 2012.

"It's going to be a l-o-o-o-ng campaign," said Michael Cole-Schwartz, a spokesman for the Human Rights Campaign.

The Minnesota Family Council, one of the primary groups pushing the amendment, announced that it hopes to raise $4.7 million to persuade Minnesotans to vote yes. "That was mentioned, but it's early in the game," said council spokesman Chuck Darrell. It's operating under an umbrella organization called Minnesotans for Marriage, which also includes the National Organization for Marriage and the Minnesota Catholic Conference.

More immediately, the council is offering training and a free admission pass to the State Fair for volunteers willing to buttonhole fairgoers and talk up the need for a vote for the amendment. Opponents of the measure also plan to flood the fairgrounds with volunteers.

"When I heard that $4.7 million figure from the other side, I said not one penny less" for us, said Donald McFarland, the campaign manager for Minnesotans United for All Families, the anti-amendment umbrella coalition, which includes OutFront Minnesota and Project 515.

No boots on the ground yet

Representatives of all the groups engaged in the fight say it's still too early to deploy ground troops, but they're increasing their efforts to enlist volunteers to blanket the state.

Family Council President John Helmberger sent an e-mail earlier this month to hundreds of thousands of church members in Minnesota, asking for ground troops.

While he predicted victory, he added that the campaign would only be successful if "people of faith [rise] up, speak, and participate in the campaign."

Darrel said the initial response to the e-mail "has been good so far, even though it's August," a deadly time to stir most political activism.

The anti-amendment forces also are blasting out e-mails to supporters. With a list of about 60,000 amendment opponents, "we're trying to get people excited and have them ready to do the work that we need to do," said Monica Meyer, OutFront's executive director.

"We know we're going to need a fair amount of time to talk to as many Minnesotans as we can."

And last week, the state AFL-CIO passed a resolution opposing the amendment, throwing organized labor's weight into the campaign.

In Minnesota, both sides have also brandished polling results.

This spring, a poll commissioned by the Family Council found that more than half of Minnesota's registered voters believe that marriage should be limited to a man and a woman -- and that three-fourths want to vote on the issue.

Amendment opponents point to a gradual swing in national polls showing that opposition to same-sex marriage is fading. A Star Tribune Minnesota Poll conducted in May found that 55 percent of those surveyed oppose adding the amendment to the state Constitution.

With anti-amendment organizations being mostly ineffective in keeping such amendments off of state constitutions, Helmberger stressed in his e-mail to churchgoers that "in every single state, voters have risen up to support traditional marriage."

McFarland agreed the climb may be steep. "We realize the odds are not in our favor, that they're against us," he said. "But this one's about Minnesota voters and this is the place to finally put a stop to it."

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